Individuals often seek to change the color of their hair. Hair dyeing products for permanently altering the color of hair typically rely on a combination of compositions. For example, compositions containing oxidative dye precursors (also known as primary intermediates or oxidation bases) and compositions containing oxidizing agents such as peroxide and persulfate compounds.
Oxidative dye precursors are often colorless or weakly colored compounds, which, when combined with oxidizing agents, transition to provide colored species via a process of oxidative condensation. The shades obtained with oxidative dye precursors may be varied by combining them with one or more couplers. Couplers include, for example, aromatic meta-diamines, meta-aminophenols, meta-diphenols, and certain heterocyclic compounds, such as indole compounds.
The oxidizing agent(s) employed in permanent dyeing compositions may degrade the melanin of the hair, which, depending on the nature of the oxidizing agent, may lead to less pronounced lightening of the fibers. Thus, for relatively weak lightening, the at least one oxidizing agent may be, for example, hydrogen peroxide. When more substantial lightening is desired, peroxygenated salts, such as persulfates, may be used, usually in the presence of hydrogen peroxide.
Hair dyeing compositions typically contain an alkalizing agent such as aqueous ammonia. The alkalizing agents activate the oxidizing agent and also cause the hair shaft to swell, thus allowing the small oxidative dye precursor molecules to penetrate the cuticle and cortex before the oxidation condensation process is completed. The resulting larger-sized colored complexes from the oxidative reaction are then trapped inside the hair fiber, thereby permanently altering the color of the hair.
The duration for which dyed hair remains colored should be limited only by hair growth rate. As new hair grows from the roots of the hair, the natural color of the hair begins to appear. Unfortunately, the color (and the quality of the color) of the artificially colored hair tends to degrade over time. For example, repeated shampooing, combing and brushing, and exposure to sunlight, oxygen, and heat, can cause the color to fade. Red colors, for instance, are particularly susceptible to these degrading processes.
An underlying problem in achieving long-lasting color durability (fade resistance) is that only a portion of oxidative dye precursor molecules are able to penetrate the cuticle and cortex before the oxidation condensation process is completed. The more deeply the coloring molecules are able to penetrate the cuticle and cortex the more durable the color. Therefore, methods for improving the color durability of artificially colored hair, for example, by discovering or developing new methods that allow coloring molecules to more deeply penetrate and permanently adhere to the hair would be welcome.